<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>


<div id="watch-example">
    <h1>观察 Watchers</h1>
    <p>
        Ask a yes/no question:
        <input v-model="question">
    </p>
    <p>{{ answer }}</p>

    <sub>在这个示例中，使用 watch 选项允许我们执行异步操作（访问一个 API），
        限制我们执行该操作的频率，并在我们得到最终结果前，设置中间状态。这是计算属性无法做到的。</sub>
    <hr />

    <h3>列表渲染：</h3>
    <ul>
        <li v-for="(item, index) in items">
            {{ parentMessage }} - {{ index }} - {{ item.message }}
        </li>
    </ul>

</div>




<script src="./lib/vue.js"></script>
<script src="https://unpkg.com/axios@0.12.0/dist/axios.min.js"></script>
<script src="https://unpkg.com/lodash@4.13.1/lodash.min.js"></script>

<script>
    var watchExampleVM = new Vue({
        el: '#watch-example',
        data: {
            question: '',
            answer: 'I cannot give you an answer!',
            parentMessage: 'parent Msg',
            items: [
                { message: 'Foo' },
                { message: 'Bar' },
            ]
        },
        watch: {
            question: function (newQuestion) {
                this.answer = 'Waiting for you to stop typing..';
                this.getAnswer();
            }
        },
        methods: {
            // _.debounce 是一个通过 lodash 限制操作频率的函数。
            // 在这个例子中，我们希望限制访问yesno.wtf/api的频率
            // ajax请求直到用户输入完毕才会发出
            // 学习更多关于 _.debounce function (and its cousin
            // _.throttle), 参考: https://lodash.com/docs#debounce
            getAnswer: _.debounce(
                function () {
                    var vm = this
                    if (this.question.indexOf('?') === -1) {
                        vm.answer = 'Questions usually contain a question mark. ;-)'
                        return
                    }
                    vm.answer = 'Thinking...'
                    axios.get('https://yesno.wtf/api')
                        .then(function (response) {
                            vm.answer = _.capitalize(response.data.answer)
                        })
                        .catch(function (error) {
                            vm.answer = 'Error! Could not reach the API. ' + error
                        })
                },
                // 这是我们为用户停止输入等待的毫秒数
                500
            )
        }
    })
</script>

</body>
</html>